This invention deals generally with stock material, and more specifically with filled hollow structures such as light poles, fence posts and pilings constructed of plastic or fiberglass.
The benefits of plastic and fiberglass for articles which are used where they are subject to corrosion are generally well recognized. Structures using such materials are light weight, strong and attractive. They can be made with color integrated into the material so that they do not need frequent painting during. their use, and possibly their greatest asset is the inherent chemical resistance of the material. A fiberglass or plastic structure such as a fence post can be expected to last as long as anyone wants it to, even in the most severe environment, with no sign of deterioration, and it will not require any maintenance.
Unfortunately, the major limitation on the availability of such pole type fiberglass or plastic structures has been the cost and difficulty involved in their manufacture. One typical method of fiberglass construction is the forming of the fiberglass into a specific shape by wrapping multiple layers of fiberglass fabric on the outside of a core and impregnating the fabric with resin or epoxy, however such manufacturing methods are very expensive because they involve a great deal of hand labor.
Another approach, particularly to the construction of cylindrical structures, is to use preformed fiberglass or plastic pipe. However, such pole structures are not strong enough for most applications unless the pipe is very thick or the structure includes wood or metal reinforcing, and both of these approaches raise the cost of fiberglass and plastic poles so that they are not competitive with conventional metal poles.
One approach to reinforcing fiberglass or plastic pipe so it can be used as a structural member has been the use of fillers which are poured into the inside of the pipe, and then harden into a core. Fillers have been suggested which include wood with an adhesive binder (U.S. Pat. No. 4,602,765 by Loper) and rigid foam or concrete (U.S. Pat. No. 3,957,250 by Murphy), but these approaches do not furnish strength comparable to metal poles.
Accordingly, there is a need to provide a fiber reinforced pole filled with a cementitious material to provide a piling having strengths similar to that of a steel piling and having surface features which create skin friction as the piling is driven into the ground, to increase bearing load capability of the pole.